How can I get some psychological help for this?

I have a feeling that I need some kind of psychological help. I keep lashing out and hitting things and pulling my hair out one minute then laughing the other.. I keep twitching and punching walls. I thought it was what all teenagers are like but its starting to scare me. last week I stabbed myself in the arm and it felt really relieving. WHAT I NEED TO KNOW.. is this just a phase.. and who should I go to to get this sorted out and can it get sorted out? I don't want to talk to anyone I know about this because I don't like discussing my problems, I find it embarrassing.
..any advice on where to go for help please?

Okay well first that is a bit out of the ordinary and also I think that you might want to at least talk to a friend about it and see what they have to say. Sometimes an outburst like that could be cause by something tragic in your life I went though it sometimes I still do but hey I dealt with it I talked to my friends and I went to a counsler...hated it but I did..
Enclosing,
Kelsey